This invention relates to arrows, and more particularly to arrowhead adapters for interchangeably mounting arrowheads on an arrow shaft to provide freedom of rotation between the arrowhead and the arrow shaft.
Previous patents have disclosed the concept of rotatably mounting arrowheads on arrow shafts, especially when broadhead hunting arrowheads are used. For example, U.S. Pat. No. 3,527,463 (Turner) suggested the use of a freely shiftable flat bladed arrowhead. This design was suggested as an alternative to arranging the arrow fletching to cause the arrow to spin in flight. By allowing the blade to "weather vane", and thus not get caught by air currents, it was thought that spinning the arrow shaft would be unnecessary. A benefit of eliminating the arrow spin was that penetration into the target was improved because there would be no rotational inertia of the spinning arrow to dissipate, which would otherwise cause the arrow to twist as it penetrated the target.
Subsequent patents disclosed the concept of allowing the arrow to spin in flight, while providing for rotation between the arrow shaft and the arrowhead. The shaft could then continue to spin though the arrowhead stopped spinning as it penetrated the target, thus preventing the effects caused by dissipation of the rotational inertia of the arrow shaft. One approach for accomplishing this was disclosed in U.S. Pat. No. 3,910,579 (Sprandel) which disclosed an arrowhead that could be mounted to swivel on a hollow arrow shaft or, as an alternative, an adapter that could be used to mount an old style broadhead so as to swivel on the shaft. Another approach, disclosed in U.S. Pat. Nos. 4,006,901, 4,093,230, 4,175,749, and 4,203,601 (Simo), included the concept of using a special broadhead constructed so that the blades can rotate around the central shaft structure of the arrowhead itself.
Old style broadheads are partially hollow, designed to fit over and be glued to the end of a solid arrow shaft. Modern broadheads are usually designed with externally threaded shanks for use with hollow shafts. Most modern archers purchase tubular arrow shafts, appropriately sized, and mount internally threaded inserts in the front end of the shafts. Thereafter, arrowheads can be interchangeably screwed into the shaft insert. This arrangement is an improvement over old style arrowheads because arrowhead alignment, essential for proper arrow flight, is more easily achieved. The archer no longer need rely on steady hands and patience to glue the arrowhead squarely on the front of the shaft.
There are commonly available adapters for converting old style arrowheads for use with modern tubular shafts and inserts. Once properly secured onto such an adapter, an old style arrowhead can be interchanged with modern arrowheads on modern arrow shafts.
The Simo device is commercially available, marketed under the trade name of "Razorbak" but the Sprandel apparatus never achieved widespread use. One problem with the Simo device is that an archer is limited to using broadheads of the design sold incorporating the patented device. Hunters cannot use their own broadheads, which they might prefer. The same problem existed for the Sprandel arrowhead.
One problem encountered with the Sprandel adapter is that it is designed for old style broadheads. There is no way to use the Sprandel device with modern arrowheads having externally threaded shanks. Perhaps more importantly, the Sprandel device suffers from a problem common to many devices that allow for freedom of rotation between the arrow shaft and arrowhead. The freedom of rotation is achieved by allowing some freeplay between the rotating parts, and thus there is a tendency for the arrowhead to droop or shift out of alignment, especially when the arrow is whipped as it is released from the bow. When broadheads are used, this lack of alignment is critical because the surface area of the blades creates a "sail" area, which affects the flight of the arrow.